1. Field of the Invention
The invention is related to the field of optical networks, and in particular, to shifting wavelengths in optical network routes to mitigate distortion in different types of fiber.
2. Statement of the Problem
Many communication companies use fiber optic cabling as a media for transmitting data because of its high bandwidth capacity. The optical fibers of a fiber optic cable can reliably transport optical signals over long distances. Optical fibers inherently have nonlinearities which cause nonlinearity effects in optical signals as the optical signals travel over the optical fiber. Some common nonlinearity effects are cross-phase modulation (XPM), self-phase modulation (SPM), four-wave mixing (FWM), stimulated Raman scattering (SRS), and stimulated Brillouin scattering (SBS). As the optical signals travel over an optical fiber, the nonlinearity effects of the optical fiber may contribute to the optical signals distorting in the optical fiber. Excessive distortion of the optical signals can unfortunately result in a loss of data being carried by the optical signals.
A typical optical network route within a long haul network or an ultra-long haul network includes a transmitter node, a plurality of fiber spans, amplifiers, regenerator nodes, and a receiver node. An amplifier or regenerator node is positioned between one or more fiber spans to compensate for signal attenuation. Typically, optical network routes are comprised of fiber spans of the same type fiber. However, some optical network routes have one or more fiber spans that are a different type of transmission fiber than the rest of the fiber spans on the route, which can be problematic.
There are currently several types of transmission fiber, such as standard Single Mode Fiber (SMF), Dispersion Shifted Fiber (DSF), and Non-Zero Dispersion Shifted Fiber (NZ-DSF). Using different types of transmission fiber in the same route can cause problems because different fibers may have different nonlinearity effects on optical signals. The different types of fibers may cause signal distortion at different wavelengths making it difficult to select which wavelengths may be used over a particular route.
As an example, a Single Mode Fiber (SMF) has a zero dispersion wavelength at about 1310 nm. A Dispersion Shifted Fiber (DSF) has a zero dispersion wavelength at about 1550 nm and a small dispersion region between 1540 nm to 1560 nm. A Non-Zero Dispersion Shifted Fiber (NZ-DSF) has a zero dispersion region from 1550 nm to 1525 nm or from 1550 nm to 1575 nm (depending on the kind of NZ-DSF). Assume an optical network route includes multiple spans of single mode fiber and one span of dispersion shifted fiber. The single mode fiber spans have strong nonlinearity effects on wavelengths at about 1310 nm. Consequently, network administrators avoid using wavelengths around 1310 nm for optical signals traveling over single mode fiber spans. The dispersion shifted fiber span has strong nonlinearity effects on wavelengths between 1540 nm and 1560 nm. Thus, network administrators avoid using wavelengths between 1540 nm and 1560 nm for optical signals traveling over the dispersion shifted fiber span.
Unfortunately, usable wavelengths are being wasted on this optical network route because different types of fiber are being used. For this optical network route, network administrators avoid wavelengths in the region of 1540 nm to 1560 nm because of the dispersion shifted fiber span, but these wavelengths are wasted on the single mode fiber spans. Wavelengths in the 1540 nm to 1560 nm region could be used on the single mode fiber spans but are not because of the high nonlinearity effects of the dispersion shifted fiber span in this region. The 1540 nm to 1560 nm region comprises much of the C-band, which is used often for carrying data. Network administrators may desire to use certain wavelengths even though one or more types of fiber in an optical network route have high nonlinearity effects at those wavelengths.